Image File Formats

Table of Contents

On this page, we will try to keep an updated list of existing image file formats and their current support level in GIMP.

Here is GIMP policy regarding image file format support:

For import: we want to support every image format, however good or bad it is. Being able to restore old images in outdated and long-forgotten formats is definitely a real use case.
For export: we want to support at least modern and most common formats.
Importing code should be lenient regarding incorrect formatting, fixing format errors automatically when possible, or optionally inquiring users if needed. Being able to salvage broken files (when feasible) is ideal.
Exporting code should be strict: files created by GIMP must conform to specs and work everywhere.

Following the principles of that policy, we organize the formats in tiers:

Top Tier support

Can be imported and exported as outlined in the policy above.

The royalty free counterpart of HEIC, using AV1 (created specifically to be royalty-free by AOMedia) image encoding and the same HEIF container format.
It supports up to 12-bit per channel, animation, HDR images and more.

Support Level

Import and Export

Implementation Notes

GIMP uses libheif for support, though there are talks that moving to libavif could be better to support some features, such as animated images (currently unsupported in GIMP). The advantage of libheif is that it also supports HEIC and more HEIF variants so we avoid additional dependencies.

BMP

Specifications

BMP

Description

Legacy image format with no or low compression and very simple to implement. There doesn’t seem to be centralized format specifications though we find various pages on the web describing its structure. From a quick skimming, the Wikipedia page itself might be all there is to know to encode and decode a BMP file.
This format is lossless.

Support Level

Import and Export

Implementation Notes

Though the format is fairly simple, it can be more featureful than first imagined since a bunch of improvements happened for GIMP 3.0, with support of:

8/16/32 bit-per-channel, integer and floating point.
2-bit indexed and ALPHABITFIELDS files.
OS/2 Huffman encoding.
RLE4 and RLE8 compressions
RLE24 (OS/2 variant of BMP compression).
Huffman (another compression variant for OS/2 BMP). The source code contains a human readable version of the Huffman code tables (generate-huffman.h). During build, the actual header huffman.h is generated which includes a digested form of these tables.
Load bmp chunk-wise instead of whole image: loads image tile-height lines at a time to reduce memory allocation for temporary image buffer.
Undefined pixels: RLE BMPs can have undefined pixels. GIMP loads those images with an alpha channel and make undefined pixels transparent.

DDS

Specifications: DDS (DirectDraw Surface)
Description: Microsoft format for storing data compressed with the previously proprietary S3 Texture Compression (S3TC) algorithm, which can be decompressed in hardware by GPUs.
It seems to be quite used in the video game industry in particular for assets such as textures and other images mapped on 3D objects.
Support Level: Import and Export
Implementation Notes: TODO

GIF

Specifications: GIF (Graphics Interchange Format)
Description: Legacy image formats which gained wide popularity on the web thanks to its small cycle animation abilities.
These last years, it slowly loses its throne to new formats such as WebP, though it is still quite omnipresent.
Support Level: Import and Export
Implementation Notes: TODO

HEIC

Specifications: HEIC
Support Level: Import and Export
Description: Modern image format, supporting up to 12-bit per channel, animation, HDR images and more, using HEVC image encoding and the HEIF container format.
Implementation Notes: GIMP uses libheif for support.
HEVC has patent issues, unlike its AVIF counterpart. This is why many Free Software distributors do not wish to package HEIC support, hence why our file-heif plug-in has runtime tests to determine support for AVIF or HEIC, making it in particular able to support some HEIF variants.

JPEG

Specifications

JPEG (Joint Photographic Experts Group)

Description

JPEG and JPEG File Interchange Format (JFIF) are legacy image formats. Similarly to GIF for small animated images, this format (in its 8-bit variant) is still the most popular format for photography on the web, despite quality issues.

Support Level

Import and Export

Implementation Notes

Both Import and Export are mandatory support in GIMP.
A lossless mode exists in JPEG, though it is so rarely implemented in various software that this format is widely considered as a lossy format. Nevertheless 8, 12 and 16-bit lossless has been implemented in libjpeg-turbo (the library we rely on) in 2022.
With jpeg-turbo >= 3.0, GIMP 3 now supports loading 12 and 16-bit per channel JPEG files (with GIMP 2.10, we only supported 8-bit JPEG, because it used to be only choose because 8 or 12-bit JPEG support at compile time.
Alternative encoding engines such as mozjpeg and/or jpegli could be added (making file size smaller for visually equivalent result), though since it makes export considerably slower, this should be an export option (not a replacement). A MR for mozjpeg exists yet relies on the upstream project to merge this patch on their side. An option for jpegli engine has not been worked on yet, as far as we know.

JXL

Specifications

Support Level

Import and Export

Description

New format, still by the Joint Photographic Experts Group, which supports lossy and lossless compression, high bit depth, and supposed to compress a lot better than legacy JPEG.

Implementation Notes

GIMP uses the reference implementation library libjxl.

ORA

Specifications: OpenRaster
Description: Meant to be an open exchange format for raster editing software. It is still a bit bare and evolution has stalled these last years. GIMP contributors originally contributed as part of its creation process.
Support Level: Import and Export

PDF

Specifications

PDF (Portable Document Format)

Description

File format for document layout. It contains vector as well as raster images, text and more.

Support Level

Import and Export

Implementation Notes

GIMP uses libpoppler for import and libcairo-pdf for export.
We consider PDF import a mandatory feature.
The poppler-data package for CJK and Cyrillic support is also mandatory because we do not consider that proper support of worldwide languages should be an “option”.
GIMP doesn’t support any of the PDF/X variants yet, but this will need to happen for good printing support. One of the Free Software with good PDF/X support is Scribus, making it a good complementary software to GIMP for doing printing jobs.

PNG

Specifications

Portable Network Graphics (PNG)

Description

Legacy compressed lossless image format, with alpha channel support.
The format supports up to 16-bit per component and proper alpha channel.
It is widely used on the web, especially for flat colored images (logos or other design) where it can even sometimes end up in smaller files (or close size, yet better quality) than JPEG, and even for photography or complex images when quality matters more than size or when transparency was required.

Support Level

Import and Export

Implementation Notes

Both Import and Export of PNG are mandatory support in GIMP.
GIMP also reads patterns in the PNG file format and it stores thumbnails as PNG images.

PSD

Specifications: PSD (Photoshop Document)
Support Level: Import and Export
Description: Core file format for Photoshop project files. A public specification is available though it is not always very complete, missing features or details.

TIFF

Specifications

Description

Legacy image format, which is well known for being able to do nearly everything.

Support Level

Import and Export

Implementation Notes

The “nearly doing anything” characteristics of TIFF is also kinda the unfortunate problem of this format as all the features are often kept very generic and several software will interpret same images differently. For instance, the “Reduced Image” feature of TIFF may be used as a thumbnail by some programs, but sometimes not. This is only one example among many.

WEBP

Specifications: WebP
Description: Modern image format, supporting lossy and lossless compression, animation and transparency. It is often described as a replacement for GIF, JPEG and PNG, but not that much further as it doesn’t support high bit depth or many color models. This makes it good for web usage, but less for advanced image usages where other recent formats make take the higher road.
Support Level: Import and Export
Implementation Notes: GIMP supports this format through the libwebp reference library.

Basic Tier support

Can be only imported or only exported as outlined in the policy above.

HEJ2

Description: JPEG 2000 encoding inside the HEIF container.
Support Level: Import only

JP2/J2K

Specifications

Description

New-ish format, still by the Joint Photographic Experts Group, which supports lossy and lossless compression, high bit depth (up to 38-bits per channel!). It compresses a bit better than legacy JPEG but this is not really its focus.
This format clearly didn’t gain a lot of popularity, at least towards the general public. Its biggest usage though is for the cinema market as it is the image format used for image tracks in the DCP container format, which is the de-facto standard in the cinema industry these days as it replaced films reels in theaters using digital movie projectors.

Support Level

Import only (JPEG 2000 images and codestreams)

Implementation Notes

GIMP uses OpenJPEG, one of the reference implementations, having moved away from libjasper for GIMP 2.10.

There is a 3P plug-in for export: https://github.com/adv-sw/gimp_j2k

MNG

Specifications: MNG (Multiple-image Network Graphics) Format
Description: Yet another variation of PNG, specifically dedicated at supporting animated files. Unlike APNG, this format was developed by the PNG development group and had therefore better early support, though usage now is limited.
Support Level: Export only

SVG

Specifications

Scalable Vector Graphics (SVG) 1.1

Description

Standard vector format, still evolving.

Support Level

Import only

Implementation Notes

Though GIMP is not primarily a vector software, considering how important this format is, the ability to rasterize SVG images is a mandatory feature.
GIMP also uses SVG for import and export of paths and it also loads gradients from SVG files.
We currently use librsvg as our backend library, which became problematic when they moved to Rust, because Rust does not support all architectures (so our requirement for having SVG support as mandatory feature clashes with our requirement for having GIMP available everywhere). Attempt to find another reliable SVG library has not been successful so far. Eventually moving to CTX when it will be more featureful regarding SVG support is also a possibility.

WBMP

Specifications: Wireless Bitmap
Support Level: Import only

WMF

Specifications: Windows Metafile Format
Support Level: Import only

Not supported yet

AI

Specifications: Adobe Illustrator Artwork
Support Level: None
Implementation Notes: The plug-in should handle the pure AI content, since .ai files normally have PDF data as compatibility layer (this one to be handled by file-pdf).

APNG

Specifications: APNG
Description: Extension of the PNG format, adding support for animated images. It is backward compatible with PNG-supporting software where it would simply show the first frame instead of an animation.
Support Level: None (WIP)
Implementation Notes: While adoption was stalling for years, it gained more support across browsers recently. It is not supported in GIMP yet. The biggest reason is that the recommended library is a patched libpng, using the same namespace as legacy libpng and not distributed commonly by distributions. This is apparently how it is shipped, bundled, in Firefox historically.
Nevertheless it seems that some browsers, like Chromium, have managed to support it using only legacy libpng.

CAL

Specifications: Continuous Acquisition and Life-cycle Support Type 1 format
Support Level: None

DNG

Specifications: Digital Negative (DNG)
Description: Gormat, proposed by Adobe, aiming to become a standard for storing raw data from digital cameras.
Support Level: None
Implementation Notes: As for most other “RAW image formats”, GIMP doesn’t support them natively anymore and instead promotes passing through a RAW image developer, such as darktable or RawTherapee. GIMP has an infrastructure system redirecting automatically RAW images to one of these software if available, then get the result back for further processing. Other RAW developer software may be added to GIMP by creating proper plug-ins with a GimpLoadProcedure flagged with the gimp_load_procedure_set_handles_raw() function.

EMF

Specifications: Enhanced Metafile Format
Support Level: None

FLIF

Specifications: Free Lossless Image Format
Support Level: None

JNG

Specifications: JNG (JPEG Network Graphics) Format
Support Level: None
Implementation Notes: Maybe the MNG plug-in could be extended? Or should it be a dedicated JNG plug-in.